Method of calibrating a system for detecting contact of a glide head with a recording media surface

ABSTRACT

A method and apparatus for calibrating a glide head and detector system performs a pre-screening to ensure the quality of the glide head and the piezoelectric sensor in the detection system. The glide head and the piezoelectric sensor detect a signal when the glide head makes contact with the disk, such as a magnetic recording disk. Calibration of the detection system utilizes a specially made bump disk that has asperities of desired height and size that protrude out of a flat disk surface. The glide head is flown over the bump disk, and by gradually reducing the disk spinning velocity, the head is brought closer to the disk and eventually into contact with the asperity. The onset of contact, as detected by the piezoelectric sensor, defines a disk spinning velocity for the head to fly at the desired height. In order to decouple the glide head flying characteristics and the piezoelectric quality and transfer function from other factors that affect the calibration of the detection system, laser pulses are directed at the glide head. Head vibrations are introduced in the glide head and detected by the piezoelectric sensor. The head excitations are recorded as a spectrogram in which the resonance frequencies are observed. From the amplitude and frequency readings, head resonance frequencies are identified and the piezoelectric sensor response is characterized. This allows the pre-screening of the head/sensor system and the decoupling of the glide head flying characteristics and the piezoelectric sensor quality from the asperity integrity effects on the calibration of the detection system.

This application is a divisional of application Ser. No. 09/121,595filed Jul. 24, 1998, now U.S. Pat. No. 6,142,006

CROSS-REFERENCE TO RELATED APPLICATIONS

This application via its continuity with 09/121,595, also claimspriority from provisional patent application Ser. No. 60/057,019, filedJul. 25, 1997, entitled NON-CONTACT GLIDE HEAD CALIBRATION WITH A PULSELASER, which is incorporated herein by reference.

1. Field of the Invention

The present invention is related to the field of glide head assembliesadapted to detect asperities which project above a specified height frommoving surfaces, and more particularly, to method and apparatus forcalibrating the glide head and detection system.

2. Background of the Invention

Hard disk drives are used in most modern computer systems to store andretrieve programs and data. The hard disks are magnetic disks which arepermanently enclosed in the hard disk drive to prevent contamination.Generally, the hard disk drive includes a spindle on which the disks aremounted and rotated with a selected angular velocity. The hard diskdrives include a magnetic head that is translated across the surface ofthe disk to allow for access to a selected annular track. The magneticdisks are typically journaled for rotation about the spindle of the harddrive in a spaced relationship to one another. A tracking arm isassociated with each disk and the read/write head is mounted to thistracking arm for accessing the desired information. These magnetic headsare typically referred to as “flying” data heads because they do notcontact the surface of the disk during rotation. Rather, the magneticheads hover above the surface on an air bearing that is located betweenthe disk and head which is caused by rotation of the disk at highspeeds.

A persisting problem with rigid magnetic memory disks is thatasperities, which are essentially protrusions on the surfaces of thedisks, may cause an anomaly when encountered by the head during highspeed revolutions. These asperities can cause errors in the transfer ofinformation or even damage to the head. In effort to reduce theoccurrences of asperities, manufacturers commonly burnish the memorysurfaces of the disk to remove asperities. In the burnishing process, aburnishing head, rather than a magnetic read-write head, is mounted in asimilar manner relative to the disk as discussed above. Burnishing headsmay be designed as either “flying” heads which pass over the surface tobe burnished or they may be designed as “contact” burnishing heads whichhave a contact surface that directly engages the asperities. During theburnishing process, the burnishing head operates to smooth out thesurface protrusions.

The next step in further refining magnetic (or optical) disks forproduction is detecting any unwanted asperities which remain after theburnishing operation and is accomplished through the use of a glidehead. The purpose of a glide head is to detect, via proximity or bycontact, any remaining asperities which may come into contact with thewrite data head during use. Glide heads are, thus. required to hover anddetect asperities which are located above specified data head flyingheights. Glide heads dynamically test the integrity of a disk'ssurfaces.

The continuous trend in the magnetic media industry is towards requiringmagnetic recording disks to have ever increasing recording densities.Accordingly, for manufacturers to develop production quality rigidmemory disks for use in this industry and the computer industry ingeneral, it is necessary to utilize glide heads that have more sensitiveresponse characteristics. Existing glide heads have inherent problemsassociated with them because it is difficult to precisely control theelectrical response characteristics of these devices.

The electrical response of a glide head is dependent upon detectionparameters of amplitude, frequency, and signal to noise ratio (S/N).However, because the industry's demands for higher magnetic densitiesrequires a lowering of the data head's flying height over the surface ofthe magnetic disks, it becomes more difficult to tighten the physicaltolerances of glide heads and effectively control the frequency,amplitude and signal to noise ratio. Current glide head designs, forexample, rely predominantly on the function of an accelerometer tocontrol these detection parameters. Unfortunately, these designs arebecoming less effective at detecting asperities as demands increase andthey are increasingly susceptible to physical and thermal stressesduring shipping and use.

In the past, it has been known to employ a glide head, whose slidecomponent is that portion of the glide head which directly contacts thesurface asperities, that is configured to include a lateral wing portionthat has a layer of piezoelectric material adhered thereto. As theslider comes into contact with a surface asperity, it leads to anexcitation of all the natural internal vibrations of the glide head/PZTassembly. The particular disturbances of the PZT sensor causes a voltageoutput from the crystalline lattice of the piezoelectric material. Partof this electrical signal, in the frequency window of the electronicfilter in use, is then monitored as an r.m.s (root-mean-square) value.Typically, one sets a threshold r.m.s voltage over which discs arerejected for improper surface finish. The problem is that since allglide heads are manufactured with a certain geometric tolerance, theyall have a different transfer function, i.e., they all responddifferently in both frequency and amplitude to a given impact asperity.It is therefore critical to calibrate precisely the response of eachindividual glide head.

The current glide technology uses the glide head and piezoelectricsensor to detect a signal upon head-disk contact. The detection systemis traditionally calibrated by utilizing a specially made “bump disk”which has asperities of desired height and size that protrude out of aflat disk surface. The asperities are either deposited via sputteringtechniques or formed by laser texturing techniques, for example. A glidehead is then flown over the bump disk. By gradual reduction of the diskspinning velocity, the glide head is brought closer to the disk andeventually comes into contact with the asperity. The onset of contact,as detected by the piezoelectric sensor, defines the specific diskspinning velocity for the head to fly at the desired height.

One of the problems with this calibration technique, however, is thatthe calibration may be affected by a number of different factors. Theseinclude the asperity integrity, the glide head flying characteristics,the quality of the piezoelectric sensor, and the transfer function. Thecombined effects of these different factors are complex and extremelydifficult to decouple.

SUMMARY OF THE INVENTION

There is a need for a method and apparatus that ensures the quality ofthe glide head and the piezoelectric sensor so that any effects on thecalibration of the detection system due to the quality of the glide headand piezoelectric sensor may be accounted for during the calibrationprocess.

This and other needs are met by embodiments of the present inventionwhich provide an arrangement for calibrating a glide head and detectorsystem comprising a radiant energy generator and means for calibratingthe glide head and detector system with radiant energy generated by theradiant energy generator. In certain embodiments, the radiant energygenerator is a pulse laser that produces laser pulses. These laserpulses are focused by a pulse laser delivery system onto a surface ofthe glide head. The laser pulses excite the glide head at glide headexcitation frequencies. The controlled laser pulses impinge upon theglide head either by thermal shock or by photon pressure shock, tointroduce vibrations in the glide head. These vibrations can be detectedby a piezoelectric sensor. The arrangement of the glide head anddetector can be characterized easily and precisely, as the inputexcitations are extremely controllable by this arrangement. Thisprovides the advantage of eliminating uncertainties introduced by thecurrent calibration technique and can be used to pre-screen the glidehead and detector system. Once the head resonance frequencies areidentified and the piezoelectric sensor response is characterized, thesefactors can be filtered or compensated for when the detection system iscalibrated.

The earlier stated needs are also met by another embodiment of thepresent invention which provides a method of calibrating a detectionsystem for detecting the contact of a glide head with a recording mediasurface. The method comprises the steps of directing a laser beam toimpinge on a surface of a glide head. A response to the glide head tothe impingement of the laser beam is then measured. A calibrationcharacteristic of the glide head is then determined based upon themeasured response.

One of the advantages of the method of the present invention is that thetechnique to pre-screen the quality of the glide head in thepiezoelectric sensor is a non-contact method and is non-intrusive to theglide head. By using an excitation that is extremely controllable, thehead/sensor system is characterized easily and precisely to eliminatethe uncertainties introduced by the combined effects of asperityintegrity, glide head flying characteristics and piezoelectric sensorquality and transfer function.

Additional features and advantages of the present invention will becomereadily apparent to those skilled in this art from the followingdetailed description, wherein embodiments of the invention aredescribed, simply by way of illustration of the best mode contemplatedfor carrying out the invention. As will be realized, the invention iscapable of other and different embodiments, and several details arecapable of modifications and various obvious respects, all withoutdeparting from the invention. Accordingly, the drawings and descriptionare to be regarded as illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The file of this patent contains at least one drawing executed in color.Copies of this patent with color drawing(s) will be provided by thePatent and Trademark Office upon request and payment of the necessaryfee.

FIG. 1 is a diagrammatic side view of a pair of glide head assemblies inaccordance with the prior art and depicting the glide head assemblies inuse to detect the presence of asperities on opposite moving surfaces ofa magnetic disk.

FIG. 2 is a perspective view of the construction of the upper glide headassembly represented in FIG. 1 and showing, in phantom, an alternativeposition for the piezoelectric transducer as it would be located for alower guide head assembly in FIG. 1.

FIG. 3 is a schematic block diagram of an arrangement to calibrate aglide head in a non-contact manner in accordance with embodiments of thepresent invention.

FIG. 4 is a depiction of a glide head as viewed in the direction ofarrow A of FIG. 3.

FIG. 5 is an exemplary frequency pattern of head excitations recorded asa spectrogram in which the vertical axis represents time and thehorizontal axis represents frequency.

FIGS. 6A, 6B, 7A and 7B are exemplary time and frequency patterns of ahead signal without and with laser pulse impingement.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention broadly relates to the calibration of a system todetect signals upon contact between a flying head and a data recordingdisk. Typically, current glide technology involves the use of a glidehead and piezoelectric sensor that detects the signal upon head-disccontact. The traditional calibration of the detection system utilizes aspecially made “bump disk” which has asperities of desired height andsize that protrude out of the flat disk surface. The onset of head-diskcontact, as detected by the piezoelectric sensor, defines the specificdisk spinning velocity for the head to fly at the desired height. Thecalibration technique is affected by a number of factors, including theflying characteristics of the glide head and the quality and transferfunction of the piezoelectric sensor. The present invention calibratesthe glide head in a noncontact manner so that the glide head andpiezoelectric sensor response can be characterized and decoupled fromthe calibration of the detection system.

FIG. 1 depicts an exemplary arrangement of a pair of glide headassemblies 10 and 12 that are used in detecting the presence ofasperities on opposite surfaces of a rigid magnetic memory disk 20 thatis journaled for rotation about spindle 26. While FIG. 1 only depicts adetection apparatus associated with a single rigid memory disk 20, itshould be appreciated that a plurality of rigid memory disks could berotatably journaled about spindle 26 with each of these memory diskshaving an associated pair of glide head assemblies.

The arrangement of FIG. 1 is exemplary only to depict one arrangement toexplain the operation of the present invention to such an arrangement.The present invention, however, is applicable for calibrating otherarrangements and configurations of glide heads and detection systems. Asshown in FIG. 1, each of the glide head assemblies 10 and 12 has anassociated support structure and is adapted for use with a system fortesting one of the moving surfaces of rigid memory disk 20.Specifically, an upper glide head assembly 10 is employed to detect thepresence of asperities on an upper surface 22 of the rigid memory disk20. Upper glide head assembly 10 is mounted to a support structure 14and communicates the detection results, via electrical lead 17, to asystem that includes signal processing circuit 19. The signal processingcircuit 19 includes standard monitoring circuitry as known in the artwith filtering circuitry capable of selecting a desired bandwidth formonitoring. Similarly, a lower glide head assembly 12 is employed todetect the presence of asperities on a lower surface 24 of rigid memorydisk 20. Lower glide head assembly 12 is mounted to a lower supportstructure 16 and communicates detection results, via electrical leads18, to signal processing circuit 19.

In FIG. 2, the representative upper glide head assembly 10 comprises aflexure 30 and glide head structure 50. Flexure 30 includes a proximalend portion 32 which is adapted to be mounted to the support structure14 in FIG. 1 by a mounting bracket 34 that is provided with a pair ofspaced apart securement holes 35 and 36. A distal end portion 38 offlexure 30 is adapted to be positioned in proximity to the upper movingsurface 22 of rigid memory disk 20. Flexure 30 extends along alongitudinal axis “L” and includes a pair of spaced apart, upstandingside walls 40, 42 which are symmetrical about longitudinal axis “L” andconverge from proximal end 32 toward distal end 38. Flexure 30 alsoincludes a tongue 44 which is mounted to the flexure 30 and forms adistal end portion 38.

As also shown in FIG. 2, the glide head structure 50 of upper glide headassembly 10 broadly includes a slider 60 that projects downwardly from alower surface 46 of flexure 30 and a piezoelectric transducer 70 whichis partly sandwiched between slider 60 and tongue 44. Piezoelectrictransducer 70 is configured as a flat plate and has an exposed free endportion 72 which projects outwardly from an outer region between distalend portion 38 and slider 60 to define a cantilever having a selectedlength “d” and a selected width “w”. The exposed free end portion 72projects laterally of distal end portion 38.

A pair of electrical leads 17 are respectively connected to the upperand lower surfaces 74 and 76 of piezoelectric transducer 70. Layers ofgold conducting material may be provided for these connections. Theelectrical lead 17 operates to communicate electrical signals to signalprocessing unit 19. A sleeve 28 is disposed longitudinally along anupper surface 48 of flexure 30 and this sleeve 28 operates to receiveand support electrical lead 17. A pair of mounting U-brackets 25 andbracket 29 are, respectively, affixed to the proximal end portion 32 andthe distal end portion 38 of flexure 30 for this purpose. In addition,bracket 27 is also provided on the upper surface 48 to help receivablyretain sleeve 28 so that the integrity of electrical signals produced byupper glide head assembly 10 is not jeopardized by any unnecessarymovement of electrical leads 17 during operation.

It should also be appreciated from FIG. 2 that the constructions oflower glide head assembly 12 would be identical to that described hereinwith reference to upper glide assembly 10 with the exception that thepiezoelectric transducer 70′ associated with lower glide head assembly12 would extend laterally outwardly from an opposite side of flexure 30and that the electrical lead 17′ which is associated therewith could besupported by U-bracket 25′ positioned at the proximal end end portion 32of flexure 30.

In operation, an asperity on the surface 22 of the disk 20 will contacta slider 60 so that it is urged upwardly. This disturbance results in acompressive force being exerted on a portion of the piezoelectrictransducer 70. This compressive force disturbs the crystalline latticeof piezoelectric transducer 70 thereby causing an electrical signal tobe generated in an electrical lead 17, these signals being communicatedback to the signal processing unit 19. However, it should also beappreciated that a variety of other electronic signals are alsogenerated by virtue of the detection of an asperity. For example, thedisturbance causes the forced vibration within flexure 30 and generatesan appreciable amount of noise in the system. These signals dampenfairly rapidly. More importantly, though, the disturbance also resultsin the generation of an electronic signal by virtue of the cantileveredorientation of piezoelectric transducer 70 which acts as a moment armand begins to vibrate at a dominant amplitude in frequency. Each of thevarious electronic signals, which have different frequency and amplitudecharacteristics, are communicated to the signal processing unit 19 wherean appropriate bandpass filter may be applied to select the dominantmode.

In the prior art, the specific characteristics and vibration frequenciesof the glide head, as well as the quality of the piezoelectric sensorand its transfer function, were not known for individual glidehead/sensor systems. In certain known arrangements, the performancecharacteristics of the glide head assembly may be varied by altering thedimensional parameters of the individual components of the assembly.However, the testing and calibration of the characteristics and qualityand transfer function of the glide head and the piezoelectric sensor hasbeen difficult to decouple from the other factors, such as the asperityintegrity.

An arrangement for calibrating a glide head and detector system inaccordance with the embodiments of the present invention is depicted inFIG. 3. This arrangement may be employed to calibrate glide head anddetector systems of different configurations, not just the particularexemplary configuration depicted in FIGS. 1 and 2. The arrangement ofthe present invention does not replace the current technique ofcalibrating a detection system using a specially made bump disk havingasperities that protrude out of the flat disk surface. Instead, thepresent invention enhances such a technique by providing a pre-screeningthat ensures the quality of the glide head and the piezoelectric sensor.As will be seen. this pre-screening is non-contact in nature and is alsonon-intrusive to the glide head.

The present invention pre-screens the glide head in the piezoelectricsensor by using controlled laser pulses directed to impinge upon thehead-sensor system. A pulse laser 80 generates radiant energy in theform of laser pulses. An exemplary pulse laser is a Nd-YVO₄ type pulselaser, although other types of lasers may be used, or other radiantenergy generators may also be used in the present invention withoutdeparting from the scope of the invention.

Exemplary values for the laser pulses are 0.1-0.2 μJ of power, withlaser pulse durations of 30 ns, at a frequency of 1.064 microns.However, these values should be considered exemplary only, as otherlaser parameters may be used to calibrate the glide head and detectorsystem, as will be appreciated by those of skill in the art.

The laser pulses are attenuated by an attenuator 82 and reflected off amirror 84 to a focusing lens 86. With proper selection and positioningof lens 86, as known to those skilled in the art, the laser pulses maybe sized and directed to impinge upon any given location of the glidehead 60. When the laser pulses impinge upon the glide head 60, either bythermal shock or photon pressure shock, vibrations in the glide head 60are introduced. The crystalline lattice of the piezoelectric transducer70 is disturbed, causing an electronic signal to be generated in theelectrical leads 17. These signals are communicated to an amplifier 88in the signal processing unit 19.

The input excitation is extremely controllable by controlling the outputof the pulse laser 80. Hence, the glide head and piezoelectric sensorsystem can be characterized easily and precisely. This allows someuncertainties introduced by current calibration techniques to beeliminated, while also pre-screening the head and sensor system. Aspectrum analyzer 90 receives the signals from the amplifier 88 in thesignal processing unit 19. A suitable spectrum analyzer 90 is anHP89410A spectrum analyzer produced by Hewlett Packard, of Palo Alto,Calif. The spectrogram produced by the spectrum analyzer 90 records thehead excitations with a vertical axis representing time and a horizontalaxis representing frequency. An exemplary spectrogram produced byspectrum analyzer 90 is depicted in FIG. 5. In this figure, when thelaser 80 is turned on so that the laser pulses impinge upon the glidehead 60, (see FIG. 4, for example), several head excitation frequenciesthat correspond to slider body resonance frequencies are observed. Theexcitation frequencies disappear when the laser 80 is turned off andreappear when the laser 80 is turned on. The pattern of head excitationfrequencies is very repeatable. From these amplitude and frequencyreadings produced in the spectrogram, the head resonance frequencies areidentified very precisely and the piezoelectric sensor response can besuitably characterized by those skilled in the art.

FIG. 6 depicts the time and frequency pattern of the head signal withoutlaser excitation. FIG. 7 depicts the time and frequency pattern of thehead signal with laser excitement. These patterns are exemplary only,however, as a different head will produce different patterns, asrecognized in the present invention.

Once the head resonance frequencies are identified and the piezoelectricsensor response characterized, in accordance with the present invention,these effects may be compensated for (e.g. filtered) in the calibrationof the detection system when the glide head is flown over the bump disk.In other words, since the glide head flying characteristics and thepiezoelectric sensor quality sensor and function are known, thecalibration of the detection system will depend only upon the asperityintegrity. Hence, the glide head flying characteristics and thepiezoelectric sensor quality and transfer function have been decoupledfrom the calibration detection system. With the present invention, thepre-screening technique that ensures the quality of the glide head andthe piezoelectric sensor is non-contact and non-intrusive to the head,while allowing the head/sensor system to be characterized easily andprecisely.

Only a preferred embodiment of the invention and but a few examples ofits versatility have been shown and described in the present disclosure.It is to be understood that the present invention is capable of use invarious other combinations and environments and is capable of changesand modifications within the scope of the inventive concept as expressedherein.

What is claimed is:
 1. A method of calibrating a detection system fordetecting contact of a glide head with a recording media surface,comprising the steps of: directing a laser beam to impinge on a surfaceof the glide head; measuring a response of the glide head to theimpingement of the laser beam; and determining a calibrationcharacteristic of the glide head based upon the measured response. 2.The method of claim 1, wherein the glide head is mounted on an arm. 3.The method of claim 2, wherein the glide head is coupled to apiezoelectric transducer that measures vibrations of the arm, thevibrations of the arm following impingement of the laser beam on theglide head surface being a function of the response of the glide head.4. The method of claim 3, wherein the glide head has excitationfrequencies corresponding to glide head resonance frequencies andwherein the step of measuring a response of the slide head includesmeasuring amplitude and frequency of the glide head excitationfrequencies by measuring the vibrations of the arm.
 5. The method ofclaim 4, wherein the step of measuring a response of the glide headincludes recording glide head excitation frequencies as a spectrogram.6. The method of claim 5, further comprising identifying the glide headresonance frequencies from the amplitude and frequency of the excitationfrequencies.
 7. The method of claim 5, further comprising characterizinga response of the piezoelectric transducer as a function of theamplitude and frequency of excitation frequencies.
 8. The method ofclaim 1, wherein the step of directing a laser beam includes causinglaser pulses to impinge upon the glide head by thermal shock.
 9. Themethod of claim 1, wherein the step of directing a laser beam includescausing laser pulses to impinge upon the glide head by photon pressureshock.